WO2024222334A1 - Viscosity reducer and preparation method therefor and use thereof, and method for improving crude-oil pollution resistance of drilling fluid - Google Patents

Abstract

The present invention relates to the technical field of drilling fluids. Disclosed are a viscosity reducer and a preparation method therefor and the use thereof, and a method for improving the crude-oil pollution resistance of a drilling fluid. The viscosity reducer comprises a matrix and particles attached to the surface of the matrix and/or wrapped in the matrix, wherein the matrix comprises an oleophilic moiety and a hydrophilic moiety; the particles do not melt at 100ºC or lower; and the number of the particles in the viscosity reducer in an area of 10*10 μm is 1-1500 according to analysis using a scanning electron microscope. The viscosity reducer can be applied to an oil-based drilling fluid and a synthetic drilling fluid to improve the crude-oil pollution resistance of the drilling fluids; and the viscosity reducer can also be used in a drilling fluid permeated by crude oil, so as to alleviate the problem of thickening caused by crude oil permeating the drilling fluid, such that the drilling fluid has reduced structural viscosity, and maintains good rheological properties.

Description

Viscosity reducer, preparation method and application thereof, and method for improving anti-oil pollution capability of drilling fluid

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Chinese patent application 202310474265.4 filed on April 27, 2023, the contents of which are incorporated herein by reference.

Technical Field

The invention relates to the technical field of drilling fluids, and in particular to a viscosity reducer and a preparation method and application thereof, and a method for improving the anti-oil pollution capability of drilling fluids.

Background Art

The widespread use of synthetic drilling fluids has attracted more and more attention to the research and application of drilling fluid treatment agents. This has also promoted the improvement of drilling fluid technology and application level to a certain extent, making the drilling fluid system more and more perfect, meeting the needs of safe, smooth and efficient drilling under a variety of different construction conditions. In recent years, although there have been many studies on drilling fluid viscosity reducers, there are few products with significant breakthroughs in performance, put into production and application, and there are still many limitations in the research, and the coverage is still relatively narrow. In particular, there are still many gaps in the work of reducing the viscosity of drilling fluids invaded by high-viscosity and high-viscosity crude oil.

After crude oil invades oil-based drilling fluid/synthetic-based drilling fluid, the drilling fluid thickens and even loses fluidity, affecting the normal circulation of the drilling fluid. In the prior art, the treatment method for crude oil invading drilling fluid usually adopts dilution method or replacement method, but the treatment cost of this method is high and the environmental pressure is relatively large. To solve the problem of deterioration of drilling fluid rheology caused by crude oil invading drilling fluid, it is necessary to have good adaptability to drilling fluid while having a good viscosity reduction effect on crude oil. CN106318348A discloses a drilling fluid that resists heavy oil pollution. Through the reasonable compounding of water, sodium bentonite, sodium carbonate, sodium carboxymethyl cellulose, low-viscosity polyanionic cellulose, fluid loss reducer A, sulfonated phenolic resin, sulfonated lignite, industrial salt, emulsifier B, emulsifier C and barite, it can maintain good rheology and improve the capacity limit of heavy oil. After the drilling fluid is contaminated by 25% heavy oil, it still has good rheology and fluid loss. However, this drilling fluid has great limitations, and there is still a lack of effective means to reduce the viscosity of oil-based drilling fluids/synthetic-based drilling fluids when crude oil invades.

Summary of the invention

The purpose of the present invention is to overcome the problem in the prior art that crude oil intrudes into oil-based drilling fluid/synthetic-based drilling fluid, resulting in thickening of drilling fluid and poor fluidity, and to provide a viscosity reducer and a preparation method and application thereof, as well as a method for improving the anti-oil pollution ability of drilling fluid. The viscosity reducer can improve the anti-oil pollution ability of drilling fluid and enable the drilling fluid invaded by crude oil to maintain good rheological properties.

In order to achieve the above object, the present invention provides a viscosity reducer in the first aspect, comprising a matrix, and particles attached to the surface of the matrix and/or encapsulated in the matrix, wherein the matrix comprises a lipophilic part and a hydrophilic part; the particles are heated to 100°C and The viscosity reducer does not melt, and according to a scanning electron microscope analysis, the number of the particles in the viscosity reducer in an area of 10 μm×10 μm is 1-1500.

Preferably, in the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 700±50 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2920±70 cm ^-1 is not less than 0.25, preferably 0.25-0.4.

The second aspect of the present invention provides a method for preparing a viscosity reducer, comprising: mixing a matrix with particles in a molten state and then drying; the matrix comprises a lipophilic portion and a hydrophilic portion; the particles do not melt below 100°C and the diameter of the particles is 300nm-5μm, and the mass ratio of the matrix to the particles is 1:(0.01-0.09).

A third aspect of the present invention provides use of the above viscosity reducer in reducing the viscosity of crude oil invading drilling fluid.

A fourth aspect of the present invention provides a method for improving the oil-resistance of drilling fluid, the method comprising adding the above-mentioned viscosity reducer to the drilling fluid.

Preferably, the amount of the viscosity reducer is 0.05-1 part by weight, preferably 0.1-0.5 part by weight, relative to 100 parts by weight of the drilling fluid.

After crude oil invades oil-based drilling fluid/synthetic drilling fluid, when the drilling fluid temperature decreases, wax crystals in the oil phase precipitate and crystallize, causing the drilling fluid to thicken and even lose fluidity, affecting the normal circulation of the drilling fluid. The viscosity reducers used in existing oil-based drilling fluid/synthetic drilling fluid are generally used to reduce the viscosity of clay particles, and do not have a wax-proof effect, and cannot reduce the viscosity of oil-invaded drilling fluid. The crude oil viscosity reducers commonly used in conventional oil field production, pipeline oil transportation, etc., considering the viscosity reduction effect on crude oil, have poor compatibility with oil-based/synthetic drilling fluids and are easy to affect the electrical stability of the drilling fluid.

The viscosity reducer provided by the present invention includes a matrix, and particles attached to the surface of the matrix and/or wrapped in the matrix. With the help of the lipophilic part and the hydrophilic part in the matrix, the viscosity reducer can penetrate into the oil sample in the drilling fluid, and help the particles and the matrix to be compounded through strong physical adsorption. The particles can maintain the particle morphology below 100°C, and can provide heterogeneous nucleation sites for wax crystals before the wax crystals precipitate and crystallize. Through the synergistic effect of the matrix and the particles, they are distributed in the oil phase in the form of micro-nano composite particles, without affecting the emulsification stability of the drilling fluid, resulting in changes in the wax precipitation characteristics of the oil sample in the drilling fluid, so that the wax crystals in the oil phase can form wax crystal floccules with larger size and more compact structure, greatly reducing the interface area between the wax crystals and the oil phase, and it is difficult to overlap each other to construct a three-dimensional wax crystal network structure wax crystal floccules, thereby effectively preventing the drilling fluid viscosity from increasing. Preferably, the viscosity reducer provided by the present invention can prevent the oil-invaded drilling fluid viscosity from increasing, and can also help improve the electrical stability of the drilling fluid.

The viscosity reducer can be applied to oil-based drilling fluids and synthetic-based drilling fluids to improve the ability of drilling fluids to resist oil pollution, and can also be used in drilling fluids invaded by crude oil to reduce the thickening problem caused by the invasion of crude oil into the drilling fluid, thereby reducing the structural viscosity of the drilling fluid and maintaining good rheological properties. The oil-soluble viscosity reducer of the present invention has a simple production process, low price, and no secondary pollution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a ¹ H NMR spectrum of polymer C1 prepared in Example 1 of the present invention;

FIG2 is an infrared absorption spectrum of polymer C1 obtained in Example 1 of the present invention;

FIG3 is a gel permeation chromatogram of polymer C1 obtained in Example 1 of the present invention;

FIG4 is a SEM image of the particles used in Example 1 of the present invention;

FIG5 is a surface SEM image of the viscosity reducer prepared in Example 1 of the present invention;

FIG6 is a cross-sectional SEM image of the viscosity reducer prepared in Example 1 of the present invention;

FIG. 7 is an infrared absorption spectrum of the viscosity reducer prepared in Example 1 of the present invention.

DETAILED DESCRIPTION

The endpoints and any values of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, the endpoint values of each range and the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

The first aspect of the present invention provides a viscosity reducer, which includes a matrix and particles attached to the surface of the matrix and/or wrapped in the matrix, wherein the matrix includes a lipophilic part and a hydrophilic part; the particles do not melt below 100° C., and according to a scanning electron microscope analysis, the number of the particles in the viscosity reducer in an area of 10 μm×10 μm is 1-1500.

According to the present invention, the viscosity reducer includes a matrix and particles. As shown in the surface SEM photo of the viscosity reducer in FIG5 , it can be seen that there are particles attached to the surface of the matrix. As shown in FIG6 , the cross-sectional SEM image of the viscosity reducer can also show that there may be particles wrapped in the matrix. With the help of the lipophilic part and the hydrophilic part in the matrix, the viscosity reducer can penetrate into the oil sample in the drilling fluid, and it is helpful for the particles and the matrix to be compounded through a strong physical adsorption effect. The particles can maintain the particle morphology below 100° C., and can provide heterogeneous nucleation sites for wax crystals before the drilling fluid temperature is reduced. The wax precipitation characteristics of the oil sample in the drilling fluid are changed through the synergistic effect of the matrix and the particles, so that the wax crystals in the oil phase can form wax crystal floccules with larger size and more compact structure. Large and dense wax crystal floccules greatly reduce the interface area between the wax crystals and the oil phase, and it is difficult to overlap each other to construct a three-dimensional wax crystal network structure wax crystal floccules, thereby effectively preventing the drilling fluid viscosity from increasing.

In the present invention, the particles in the viscosity reducer do not melt below 100°C. It is understood that after the viscosity reducer is heat treated at any temperature below 100°C, the particles therein can still maintain their particle shape. By making the particles not melt below 100°C, it can be ensured that the high-temperature drilling fluid invaded by crude oil affects the crystallization behavior of wax crystals after it is lifted to the ground and before wax crystals are precipitated, thereby effectively preventing the drilling fluid viscosity from increasing.

In the present invention, preferably, the size of the particles is 300nm-5μm, preferably 500nm-3μm. By controlling the size of the particles within the range of 300nm-5μm, it can be ensured that the particles provide heterogeneous nucleation sites for wax crystals. By controlling the size of the particles within the above preferred range, it is beneficial for the particles to have an appropriate strength of interaction with the polymer, and it is helpful for the formation of wax crystals in the oil phase. The wax crystal floccules with larger size and more compact structure further improve the viscosity reduction effect.

In the present invention, the size of the particles in the viscosity reducer refers to the maximum straight-line distance passing through the inside of the particles. The following method is used for testing: After the viscosity reducer is sampled, it is observed by scanning electron microscopy (SEM), and the size values of 10 particles in the viscosity reducer are counted and the average value is calculated, which is recorded as the particle size. The test conditions of SEM include: scanning electron microscope instrument model TESCAN MIRA LMS, test voltage 200eV-30keV, magnification 20k-100k.

The present invention has no particular limitation on the morphology of the particles, which may be spherical or non-spherical particles. Preferably, the particles are spherical particles.

In the present invention, the particles in the viscosity reducer have good dispersibility. According to scanning electron microscopy analysis, in the viscosity reducer in the area of 10 μm×10 μm, the number of the particles is 1-1500, preferably 2-1000, and more preferably 5-500. In a particularly preferred case, in the viscosity reducer in the area of 10 μm×10 μm, the number of the particles is 5-200. In the present invention, the number of particles in any 5 areas is counted, and the average value is calculated and recorded as the number of particles in the viscosity reducer. Controlling the dispersion of the particles within the above preferred range is conducive to exerting the synergistic effect of the particles and the matrix, and improving the dispersibility and viscosity reduction effect of the viscosity reducer in the drilling fluid without affecting the emulsification stability of the drilling fluid.

In the present invention, the SEM image of the untreated particles is shown in Figure 4, and the surface SEM image and cross-sectional SEM image of the viscosity reducer are shown in Figures 5 and 6, respectively. It can be seen from Figures 5 and 6 that there are particles attached to the surface of the matrix and wrapped inside the matrix in the viscosity reducer. Compared with the untreated particles, the particles in the viscosity reducer basically maintain their original morphology and size.

In the present invention, preferably, the particles are adsorbed on the surface of the matrix and/or wrapped in the matrix through hydrogen bonding to form micro-nano composite particles. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 700±50cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2920±70cm ^-1 is not less than 0.25, preferably 0.25-0.4, and more preferably 0.3-0.35. The "maximum absorption peak" refers to the absorption peak with the highest intensity in this region. The ratio of P1/P2 is within the above preferred range, which is conducive to the viscosity reducer penetrating into the crude oil wax crystal matrix and playing a role in heterogeneous nucleation, affecting the morphology and network structure of the wax, interfering with the growth of wax crystals, and achieving a viscosity reduction effect. The reason may be that due to the generation of hydrogen bonds between the matrix and the particles, there is an interaction force with appropriate strength between the particles and the matrix, and the heterogeneous nucleation effect is enhanced.

The synthesized viscosity reducer was analyzed by infrared FT-IR (Nicolet iz10, Thermol Scientific Co., USA) spectrometer. The potassium bromide (KBr) tableting method was used to grind the test product with KBr (1:100 weight ratio) to prepare tablets, and the samples required for the experiment were placed in a Fourier transform infrared spectrometer for testing and analysis.

According to some preferred embodiments of the present invention, the mass ratio of the matrix to the particles is 1:(0.01-0.5), preferably 1:(0.02-0.07), and more preferably 1:(0.03-0.05).

In the present invention, the mass ratio of the matrix and the particles can be measured by a density comparison method, and the specific operation is as follows: the density values of the matrix and the particles are tested respectively, and then a linear curve of density versus mass composition is fitted; then the density value of the viscosity reducer is tested, and the density of the viscosity reducer is substituted into the density versus mass composition curve to obtain the mass ratio of the matrix and the particles.

According to some preferred embodiments of the present invention, the melting point of the particles is 100-160° C., preferably 130-160° C. The melting point involved in the present invention refers to the melting point at 0.1 MPa.

Preferably, the particles have a density of 1-2 g/cm ³ , preferably 1-1.5 g/cm ³ .

According to some preferred embodiments of the present invention, at 20° C., the lipophilicity of the particles is not less than 50%, preferably 50-70%. In the above preferred case, it is beneficial to improve the dispersibility of the viscosity reducer in the drilling fluid.

In the present invention, the test method of lipophilicity includes: placing 1 g of particles in 50 mL of water at 20° C., and then adding methanol dropwise until the particles are completely wetted (the particles are completely immersed in methanol and do not float on the surface, which is considered to be completely wetted), recording the amount of methanol added V (mL), and calculating the lipophilicity = V/(50+V)×100%.

The present invention has a wide range of choices for the composition of the particles, preferably satisfying the above physical properties, and can be organic particles, inorganic oxide particles, or organic-inorganic composite particles, etc. The organic particles can be, for example, organic polymer particles; the organic-inorganic composite particles can be organic modified inorganic particles.

In the present invention, the hydrophilic part and the lipophilic part in the matrix have an appropriate ratio. Preferably, the hydrophilic-lipophilic balance value (HLB value) of the matrix is 3-5. Controlling the HLB value of the matrix within the above preferred range is conducive to improving the dispersibility and permeability of the viscosity reducer in the drilling fluid. In the present invention, the hydrophilic-lipophilic balance value of the matrix is measured by the distribution coefficient method.

According to some preferred embodiments of the present invention, the oleophilic part contains at least one oleophilic functional group, the hydrophilic part contains at least one hydrophilic functional group, and in the matrix, the molar ratio of the oleophilic functional group to the hydrophilic functional group is 8-90: 1. In the above preferred case, it is beneficial to reduce the viscosity of the oil-invaded drilling fluid and improve the electrical stability of the drilling fluid.

Preferably, based on the total amount of the matrix, the content of the lipophilic functional group is 80-95 wt %, more preferably 90-94 wt %.

In the present invention, the relative content of the hydrophilic and lipophilic functional groups is determined by infrared spectroscopy to determine the characteristic functional groups, and by liquid chromatography to determine the molecular weight, thereby determining the molecular structure, and then calculated according to the number of hydrophilic and lipophilic functional groups in the molecular structure.

The present invention has no particular requirements for the structure of the matrix, as long as the matrix includes a lipophilic part and a hydrophilic part. Preferably, the matrix is a polymer, and the weight average molecular weight of the polymer is 5000-50000 g/mol, preferably 6000-30000 g/mol, and more preferably 8000-20000 g/mol. In the present invention, an HLC-8321GPC gel permeation chromatograph is used, tetrahydrofuran is used as the mobile phase, and polystyrene is used as the standard sample to measure the weight average molecular weight of the polymer.

Further, the matrix may be a homopolymer or a copolymer. It is understood that when the polymer is a homopolymer, the lipophilic part and the hydrophilic part are present in the same structural unit; when the polymer is a copolymer, the lipophilic part and the hydrophilic part may be present in the same structural unit or in different structural units. Preferably, when the polymer is a copolymer, the lipophilic part and the hydrophilic part are present in different structural units.

The present invention has no special requirements for the arrangement of different structural units in the copolymer, and the copolymer can be a random copolymer, an alternating copolymer or a block copolymer.

According to the present invention, at least one lipophilic functional group is included in the lipophilic part, and the viscosity reducer is easily infiltrated into the crude oil wax crystal matrix through the lipophilic functional group, thereby affecting the wax separation characteristics of the oil sample in the drilling fluid, and improving the viscosity reduction effect. The lipophilic functional group has a conventional definition in this area, for example, it can be a substituted or unsubstituted alkyl, alkenyl, alkynyl or aryl, etc., preferably an alkyl, alkenyl, alkynyl or aryl of C16-C22. For example, hexadecyl, octadecyl, eicosyl, docosyl, hexadecenyl, octadecenyl, eicosyl, docosyl, hexadecynyl, octadecynyl, eicosyl, docosyl, decanylphenyl, undecylphenyl, dodecylphenyl, tridecylphenyl, tetradecylphenyl or hexadecylphenyl, or isomers of the above substituents.

According to a particularly preferred embodiment of the present invention, the lipophilic functional group is a C16-C22 straight chain alkyl group, such as hexadecyl, octadecyl, eicosyl or docosyl. In the above preferred case, the lipophilic part has a better matching effect with the alkyl chain length of the wax crystal, which is beneficial to further improve the ability of the drilling fluid to resist the invasion of antigenic oil and improve the viscosity reduction effect.

According to the present invention, the hydrophilic part contains at least one hydrophilic functional group. On the one hand, the hydrophilic functional group is conducive to the formation of hydrogen bond adsorption between the matrix and the particles. On the other hand, the presence of the hydrophilic functional group can avoid further aggregation of wax crystal floccules precipitated using the particles attached to the surface of the polymer as a crystallization template, thereby maintaining good rheological properties of the drilling fluid.

In the present invention, the hydrophilic functional group has a conventional definition in the art, for example, it can be a hydroxyl group, an aldehyde group, a carboxyl group, an anhydride group, an amino group, a sulfonyl group, a sulfonamide group or a carbamoyl group, preferably at least one of a hydroxyl group, a carboxyl group, an anhydride group and an amino group. In the present invention, the presence of the lipophilic functional group and the hydrophilic functional group in the matrix can be determined by infrared absorption spectroscopy.

According to some preferred embodiments of the present invention, the matrix and the particles contain the same structural unit, preferably, the same structural unit is an acrylic structural unit; preferably, in the viscosity reducer, the ratio of the molar amount of the same structural unit contained in the matrix to the molar amount of the same structural unit contained in the particles is 1-30:1, preferably 5-15:1.

According to some particularly preferred embodiments of the present invention, the polymer comprises a structural unit A as shown in formula (1) and a structural unit B as shown in formula (2);

wherein R ₁ , R ₂ , R ₃ , and R ₄ are each independently selected from a hydrogen atom, a C16-C22 alkyl group, a C16-C22 alkenyl group, a C16-C22 alkynyl group, or a C16-C22 aryl group, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ is not a hydrogen atom;

R ₅ , R ₆ , R ₇ and R ₈ contain at least one hydroxyl group, carboxyl group or amino group, or R ₅ and R ₆ are connected to form an acid anhydride, or R ₇ and R ₈ are connected to form an acid anhydride.

When the polymer in the viscosity reducer has the above-mentioned preferred structural composition, it is beneficial to further improve the resistance of the drilling fluid to oil invasion. Ability to maintain good rheological properties of drilling fluid.

Preferably, in formula (1), R ₁ is selected from C16-C22 alkyl, C16-C22 alkenyl, C16-C22 alkynyl or C16-C22 aryl, more preferably C16-C22 straight-chain alkyl, such as hexadecyl, octadecyl, eicosyl, docosyl, hexadecenyl, octadecenyl, eicosyl, docosenyl, hexaynyl, octaynyl, eicosyl, docosynyl, decanylphenyl, undecylphenyl, dodecylphenyl, tridecylphenyl, tetradecylphenyl or hexadecylphenyl, or isomers of the above substituents; R ₂ , R ₃ and R ₄ are hydrogen.

Preferably, in formula (2), _R5 and _R6 are connected to form an acid anhydride, and _R7 and _R8 are hydrogen atoms; or, _R7 and _R8 are connected to form an acid anhydride, and _R5 and _R6 are hydrogen atoms.

According to the present invention, as long as the polymer contains the above-mentioned structural unit A and structural unit B, the present invention has a wide selection range for the relative content of the structural unit A and structural unit B, so as to satisfy the substrate having suitable hydrophilicity and lipophilicity. In order to ensure that there is suitable adhesion between the polymer and the particles, and to enable the viscosity reducer to better exert the viscosity reducing effect, preferably, in the polymer, the molar ratio of the structural unit A to the structural unit B is (1-10):1, preferably (2-5):1, and more preferably (3-4):1.

The present invention has no particular limitation on the structure of the polymer. When the polymer contains the above-mentioned structural unit A and structural unit B, there is no particular requirement for the arrangement of structural unit A and structural unit B. It can be a regular block copolymer, a partially regular block copolymer or a random copolymer. In order to avoid cumbersome production processes, the polymer in the present invention is preferably a random copolymer.

In a further preferred embodiment, the particles are at least one of polymethyl methacrylate particles, polyethyl methacrylate particles, glycidyl methacrylate particles and polyethylene terephthalate particles, preferably polymethyl methacrylate particles.

Preferably, the weight average molecular weight of the polymethyl methacrylate is 15000-750000 g/mol, preferably 20000-300000 g/mol.

According to some preferred embodiments of the present invention, the polymer can be prepared by the following method: mixing a monomer a having a structure represented by formula (i), a monomer b having a structure represented by formula (ii) and a solvent, and then performing a copolymerization reaction under the action of an initiator;

R ₁ to R ₈ in formula (i) and formula (ii) have the same definitions as in formula (1) and formula (2).

Preferably, the molar ratio of the monomer a to the monomer b is (1-10):1, preferably (2-5):1, more preferably (3-4): 1.

The present invention has a wide selection range for the initiator, and any initiator known in the art that can be used to initiate the copolymerization reaction of monomer a and monomer b can be applied to the present invention. Preferably, the initiator is benzamide peroxide.

The present invention has no particular limitation on the amount of the initiator, and those skilled in the art can adjust it according to actual needs. Preferably, based on the total mass of the monomer a and the monomer b, the amount of the initiator is 0.3-1wt%, preferably 0.3-0.5wt%.

According to the present invention, the copolymerization reaction is carried out in the presence of a solvent. The present invention has no special requirements for the selection and dosage of the solvent, and the solvent is sufficient to dissolve and disperse the reaction raw materials. The solvent can be, for example, an alkane, a halogenated alkane, an aromatic hydrocarbon, a halogenated aromatic hydrocarbon, etc., for example, benzene, toluene, xylene, pentane, hexane, octane, cyclohexane, chlorobenzene, dichlorobenzene and dichloromethane, etc. Preferably, the solvent is toluene. Preferably, the ratio of the mass of the solvent to the total mass of the monomer a and the monomer b is (2-7):1.

The present invention has no particular requirements for the mixing method and conditions. Preferably, the mixing is performed under stirring conditions. The present invention also has no particular restrictions on the stirring parameters, as long as the monomer is completely dissolved in the solvent. Preferably, the stirring rate is 400-600 rpm.

Preferably, the mixing temperature is 30-60° C., preferably 40-50° C., and the mixing time is 5-20 min, preferably 10-15 min. Under the above preferred mixing conditions, it is beneficial to ensure that the monomer is completely dissolved.

According to some preferred embodiments of the present invention, the conditions of the copolymerization reaction include: reaction temperature of 50-100° C., preferably 60-80° C., reaction time of 2-12 h, preferably 5-10 h.

According to some preferred embodiments of the present invention, the preparation method comprises: mixing monomer a having a structure shown in formula (i), monomer b having a structure shown in formula (ii) and a solvent, then heating the mixture to a copolymerization reaction temperature, and then adding an initiator to carry out a copolymerization reaction.

Preferably, the copolymerization reaction is carried out under stirring conditions, and the stirring conditions may be the same as the stirring conditions in the mixing.

According to the present invention, preferably, the preparation method further comprises: purifying the copolymerization product. The purification can be carried out by conventional methods in the art, for example, by washing and purifying with an organic solvent. Preferably, the organic solvent washing and purifying process comprises: mixing the copolymerization product with a solvent, stirring until precipitation occurs, and then performing solid-liquid separation.

In the present invention, the organic solvent may be an alcohol, such as methanol and/or ethanol. The present invention has no particular requirement for the amount of the organic solvent, which is preferably in excess of the reaction product, for example, the amount of the organic solvent may be 5-10 times the mass of the reaction product.

The present invention has no particular limitation on the solid-liquid separation method, which may be a conventional operation method in the art, such as filtration.

The present invention provides a viscosity reducer, wherein the oil-soluble viscosity reducer comprises a copolymer as shown in Formula I and PMMA microspheres;

Wherein, _R1 is a C12-C30 straight chain or branched alkyl group; m is 10-50, and n is 5-30; the PMMA microspheres have a diameter of 300-500 nm and a cross-linking degree of 10-20%.

Preferably, in Formula I, _R1 is a C16-C22 straight or branched alkyl group; and/or m/n is (1-10): 1. For example, m/n is, but not limited to, 1:1, 2:1, 3:1, 5:1, 7:1, 8:1, 9:1, 10:1.

Preferably, the structure of the copolymer is as shown in Formula II,

Preferably, the weight average molecular weight of the copolymer is 5000-50000 g/mol, preferably 8000-30000 g/mol, more preferably 8000-20000 g/mol.

Preferably, the copolymer is a random copolymer.

Preferably, the mass ratio of the copolymer to the PMMA microsphere is 1:(0.01-0.1). For example, the mass ratio of the copolymer to the PMMA microsphere is, but not limited to, 1:0.01, 1:0.03, 1:0.05, 1:0.07, 1:0.09, 1:0.1.

The second aspect of the present invention provides a method for preparing a viscosity reducer, comprising: mixing a matrix with particles in a molten state and then drying; the matrix comprises a lipophilic portion and a hydrophilic portion; the particles do not melt below 100°C, and the mass ratio of the matrix to the particles is 1:(0.01-0.5).

The matrix and particles have the same definitions as described in the first aspect and will not be repeated here.

In the present invention, it is ensured that the matrix is in a molten state during the mixing, and at least part of the particles are not melted. The preferred mixing method is conducive to improving the dispersion of the particles, forming a suitable interaction force between the matrix and the particles, and further improving the viscosity reducing effect of the viscosity reducer. In the present invention, the matrix can be melted first and then mixed with the particles, or the matrix and the particles can be preliminarily mixed and then heated to melt the matrix. Preferably, the matrix and the particles can be added together into a mixing device for melt blending.

In the present invention, the mixing can be performed using conventional equipment in the art, for example, in a melt blender.

According to some preferred embodiments of the present invention, the mixing conditions include: a mixing temperature of 100-180° C., preferably 120-160° C., and a mixing time of 5-30 min, preferably 10-20 min.

Preferably, the mass ratio of the matrix to the particles is 1:(0.02-0.07), more preferably 1:(0.03-0.05).

Preferably, the drying is carried out under vacuum conditions, the drying temperature is 50-100° C., preferably 60-80° C., and the drying time is 5-15 h, preferably 10-12 h.

A third aspect of the present invention provides the use of the above viscosity reducer in reducing the viscosity of crude oil invading drilling fluid.

A fourth aspect of the present invention provides a method for improving the oil-resistance of drilling fluid, the method comprising adding the viscosity reducer described in the first aspect to the drilling fluid.

In the present invention, the viscosity reducer can be added to the drilling fluid that has not been invaded by crude oil, and can also be added to the drilling fluid during the use of the drilling fluid and after being invaded by crude oil, to improve the anti-oil pollution ability of the drilling fluid to suppress the viscosity increase of the drilling fluid after being invaded by crude oil. Since crude oil invades the drilling fluid, it is usually in an underground high-temperature environment. When the drilling fluid circulates to the ground, as the temperature decreases, the crude oil wax precipitates and crystallizes, thereby increasing the viscosity of the drilling fluid, deteriorating the fluidity, or even losing fluidity, thereby affecting the normal circulation and reuse of the drilling fluid. The viscosity reducer provided by the present invention can preferably be added to the drilling fluid after the crude oil invades the drilling fluid and between the crude oil wax precipitation and crystallization, that is, after the drilling fluid is lifted to the ground and before it is cooled, it is added to the drilling fluid, so that the wax crystals in the oil phase can be precipitated with the particles attached to the surface of the polymer as a crystallization template, thereby forming a wax crystal flocculent with a larger size and a more compact structure, avoiding the problem of overall rheological properties deteriorating caused by the invasion of crude oil into the drilling fluid.

According to some preferred embodiments of the present invention, the amount of the viscosity reducer is 0.05-1 part by weight, preferably 0.1-0.5 part by weight, relative to 100 parts by weight of the drilling fluid.

The present invention has no particular limitation on the composition of the drilling fluid, which may be conventional oil-based drilling fluid or synthetic-based drilling fluid in the art.

In the present invention, the base oil in the oil-based drilling fluid or synthetic-based drilling fluid has a wide range of types, and can be provided by the oil phase conventionally used in the art, and those skilled in the art can select it according to actual needs. Preferably, the base oil is selected from at least one of mineral oil and synthetic base oil, which is well known to those skilled in the art.

According to the present invention, the drilling fluid may also contain conventional drilling fluid treatment agents in the art, such as one or more of organic soil, emulsifier, inhibitor, plugging agent, weighting agent, wetting agent, alkaline regulator and fluid loss reducer. Those skilled in the art may make the selection according to actual needs, and the present invention has no particular limitation on this. According to some preferred embodiments of the present invention, the organic The clay may be, for example, quaternary ammonium salt-modified bentonite.

The present invention has no particular limitation on the source of the fluid loss reducer, and commercial products known to those skilled in the art can be used. For example, it can be a humic acid fluid loss reducer, an asphalt fluid loss reducer, etc. For example, it can be natural asphalt powder purchased from Shengli Oilfield Zhongsheng Petrochemical Co., Ltd.

According to some preferred embodiments of the present invention, the emulsifier may be at least one of divalent metal soap of higher fatty acid, calcium alkyl sulfonate, fatty acid emulsifier and amide emulsifier. Preferably, the emulsifier includes a primary emulsifier and an auxiliary emulsifier, and the primary emulsifier and the auxiliary emulsifier may be combined in a conventional combination manner in the art. Preferably, the mass ratio of the primary emulsifier to the auxiliary emulsifier is 1:0.3-1.

The present invention has no special requirements for the selection of the primary emulsifier and the secondary emulsifier, and those skilled in the art can select them according to actual needs. For example, the primary emulsifier can be a commercial product with the brand name HIEMUL purchased from Jingzhou Jiahua Technology Co., Ltd., and the secondary emulsifier can be a commercial product with the brand name HICOAT purchased from Jingzhou Jiahua Technology Co., Ltd.

According to some preferred embodiments of the present invention, the weighting agent may be barite and/or iron ore powder, preferably barite. The present invention has no special requirements for the amount of the weighting agent, which can be adjusted according to the drilling fluid density requirements.

According to some preferred embodiments of the present invention, the alkaline regulator may be calcium oxide.

According to some preferred embodiments of the present invention, the wetting agent can be a long-chain alkane quaternary ammonium salt organic matter. For example, the wetting agent can be a commercial product with the brand name HIWET purchased from Jingzhou Jiahua Technology Co., Ltd.

In the present invention, the amount of the emulsifier, wetting agent, fluid loss agent, alkaline regulator and organic soil can be selected according to actual needs, and the present invention has no special limitation on this. According to some preferred embodiments of the present invention, based on 100 parts by weight of the base oil, the amount of the primary emulsifier is 1-4 parts by weight, the amount of the auxiliary emulsifier is 1-2 parts by weight, the amount of the wetting agent is 0.5-2 parts by weight, the amount of the fluid loss agent is 1-5 parts by weight, the amount of the alkaline regulator is 1-5 parts by weight, and the amount of the organic soil is 1-6 parts by weight.

The present invention will be described in detail below through examples.

The main raw materials involved in the following examples and comparative examples are as follows. Unless otherwise specified, the remaining raw materials are purchased from commercial sources.

Polymethyl methacrylate (PMMA) microspheres P1: commercially available, with a microsphere diameter of 400 nm, a density of 1-1.3 g/cm ³ , a weight average molecular weight of 40,000 g/mol, and a lipophilicity of 65% at 20°C;

Polymethyl methacrylate (PMMA) microspheres P2: commercially available, with a microsphere diameter of 3 μm, a density of 1.1-1.3 g/cm ³ , a weight average molecular weight of 250,000 g/mol, and a lipophilicity of 50% at 20°C;

Main emulsifier: brand HIEMUL, purchased from Jingzhou Jiahua Technology Co., Ltd.;

Auxiliary emulsifier: brand name HICOAT, purchased from Jingzhou Jiahua Technology Co., Ltd.;

Organic clay: brand FBJS-147, purchased from Zhejiang Fenghong New Materials Co., Ltd.;

Wetting agent: brand HIWET, purchased from Jingzhou Jiahua Technology Co., Ltd.;

Fluid loss reducer: natural asphalt powder, purchased from Zhongsheng Petrochemical Co., Ltd. of Shengli Oilfield;

Alkaline regulator: brand LIM, purchased from Jingzhou Jiahua Technology Co., Ltd.;

Barite: purchased from Shengli Oilfield Wantai Industry and Trade Co., Ltd.

The specific conditions of the main tests involved in the following examples and comparative examples are as follows:

The polymer was measured by hydrogen nuclear magnetic resonance ( ¹ H NMR) spectrum at 500 MHz using a Bruker-500 AVANCE III HD nuclear magnetic resonance spectrometer from Bruker, Switzerland, with deuterated chloroform as the solvent.

The synthesized oil-soluble viscosity reducer was analyzed by infrared FT-IR (Nicolet iz10, Thermol Scientific Co., USA) spectrometer. The potassium bromide (KBr) tableting method was used to grind the test product with KBr (1:100) to prepare tablets, and the samples required for the experiment were placed in a Fourier transform infrared spectrometer for testing and analysis.

The weight average molecular weight of the polymer was determined by using HLC-8321GPC gel permeation chromatograph with tetrahydrofuran as the mobile phase and polystyrene as the standard sample.

Example 1

(1) octadecyl acrylate and maleic anhydride monomers were weighed in a molar ratio of 3:1 and added to a flask, and toluene solvent was added in a ratio of toluene to the total mass of the monomers of 3:1, the temperature of the oil bath was controlled to be 40° C. and mechanical stirring was applied at a constant rate, the stirring rate was maintained at 500 rpm, and after stirring for 10 minutes to ensure that the monomers were completely dissolved in toluene, the oil bath temperature was adjusted to a reaction temperature of 80° C., and a benzamide peroxide solution (1 wt% of the monomer mass) was added dropwise, and the reaction time was controlled to be 8 hours to obtain a reaction product;

(2) pouring the reaction product obtained in step (1) into a 500 mL beaker, adding 5 times the weight of methanol and stirring continuously until floccules precipitate on the bottom of the beaker, filtering and drying to obtain a purified polymer C1; analyzing the composition structure of the polymer C1 by hydrogen nuclear magnetic spectrum, as shown in FIG1 , as can be seen from FIG1 , the chemical shifts at δ0.9, δ1.3 and δ1.6 belong to the hydrogen proton peaks of -CH ₃ , -CH ₂ - and -CH-, respectively, the hydrogen proton peak at δ4.0 belongs to the hydrogen proton peak of -C＝O-CH ₂ -, and the hydrogen proton peak at δ3.5 belongs to the hydrogen proton peak of the maleic anhydride group. The infrared absorption spectrum of polymer C1 is shown in FIG2 , which shows characteristic spectral bands at 1470, 2920 cm ^-1 (-CH ₂ -stretching peak), 2960 cm ^-1 (-CH ₃ stretching peak) and 1740 cm ^-1 (stretching peak of C=O ester group), while 1785 and 1851 cm ^-1 are C=O characteristic peaks of anhydride group, and no characteristic peaks are shown at 1600-1680 cm ^-1 , indicating that -C=C- does not exist, indicating that the acrylate monomer and maleic anhydride undergo copolymerization reaction. The successful synthesis of octadecyl acrylate-maleic anhydride copolymer is proved.

Combined NMR and IR results show that the polymer C1 contains structural unit A represented by formula (1) and structural unit B represented by formula (2), wherein _R1 is a C18 straight-chain alkyl group, _R2 , _R3 , and _R4 are hydrogen atoms, _R5 and _R6 are connected to form anhydride, and _R7 and _R8 are hydrogen.

The GPC test characterization, as shown in Figure 3, calculated that the weight average molecular weight of the polymer C1 is 11886 g/mol. The coefficient method test shows that the hydrophile-lipophile balance (HLB value) of the matrix is 4.5.

(3) placing polymer C1 and PMMA microspheres P2 in a melt blender at a mass ratio of 1:0.03, and melt blending at 130° C. for 17 min to obtain a blend;

(4) The blend obtained in step (3) was placed in a vacuum oven and vacuum dried at 80° C. for 12 h to obtain a white block product, which is an oil-soluble viscosity reducer S1. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the acrylic acid structural units from the matrix to the acrylic acid structural units from the microspheres is 9.3:1.

The SEM image of the untreated microspheres is shown in FIG4, and the surface SEM image and cross-sectional SEM image of the viscosity reducer S1 are shown in FIG5 and FIG6, respectively. It can be seen from FIG5 and FIG6 that there are microsphere particles attached to the surface of the matrix and wrapped inside the matrix in the viscosity reducer, and the microspheres in the viscosity reducer basically maintain their original morphology and size. According to scanning electron microscopy analysis, the number of microspheres in the viscosity reducer in the area of 10 μm×10 μm is 5.

The viscosity reducer S1 was subjected to infrared absorption spectrum test, and the results are shown in FIG7 . Compared with the infrared absorption spectrum of polymer C1, it can be seen that the maximum absorption peak intensity (P1) at 705 cm ^-1 is significantly enhanced, indicating that the PMMA microspheres are combined with the polymer through hydrogen bonding.

In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) at 705 cm ^-1 to the maximum absorption peak intensity (P2) at 2915 cm ^-1 is 0.3.

Example 2

The method of Example 1 is followed, except that polymer C1 and PMMA microspheres P1 are placed in a melt blender at a mass ratio of 1:0.05, melt blended at 130°C for 11 minutes to obtain a blend; the blend is placed in a vacuum oven and vacuum dried at 80°C for 12 hours to obtain a white block product, which is an oil-soluble viscosity reducer S2. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 5.6:1.

The viscosity reducer S2 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 28 through scanning electron microscopy analysis.

The viscosity reducer S2 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 705 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2920 cm ^-1 was 0.35.

Example 3

(1) Hexadecyl acrylate and maleic anhydride monomers were weighed in a molar ratio of 3:1 and added to a flask, and toluene solvent was added in a ratio of toluene to the total mass of the monomers of 3:1, the temperature of the oil bath was controlled to be 40°C and mechanical stirring was applied at a constant rate, the stirring rate was maintained at 500 rpm, and after stirring for 10 minutes to ensure that the monomers were completely dissolved in toluene, the oil bath temperature was adjusted to a reaction temperature of 80°C, and a benzamide peroxide solution (1 wt% of the monomer mass) was added dropwise, and the reaction time was controlled to be 8 hours to obtain a reaction product;

(2) Pour the reaction product obtained in step (1) into a 500 mL beaker, add 5 times the weight of methanol and continue stirring until floccules precipitate on the bottom of the beaker, filter and dry to obtain purified polymer C2; analyze the composition structure of polymer C2 by hydrogen nuclear magnetic spectrum, and the peaks in the figure are assigned as follows: ¹ H NMR, absorption peaks at different chemical shifts represent different types of hydrogen protons. The chemical shifts at δ0.9, δ1.3 and δ1.6 belong to the hydrogen proton peaks of -CH ₃ , -CH ₂ - and -CH-, respectively, the hydrogen proton peak at δ4.0 belongs to the hydrogen proton peak of -C＝O-CH ₂ -, and the hydrogen proton peak of the maleic anhydride group is at δ3.5. That is, the hydrogen proton peak at the chemical shift of 3.5 ppm proves the successful synthesis of polymer C2.

It is proved that the polymer C2 contains the structural unit A represented by formula (1) and the structural unit B represented by formula (2), wherein _R1 is a C16 straight chain alkyl group, _R2 , _R3 , and _R4 are hydrogen atoms, _R5 and _R6 are connected to form anhydride, and _R7 and _R8 are hydrogen.

The GPC test showed that the weight average molecular weight of the polymer C2 was 10940 g/mol. The distribution coefficient method showed that the hydrophilic-lipophilic balance (HLB) value of the polymer C2 was 4.6.

(3) placing polymer C2 and PMMA microspheres P1 in a melt blender at a mass ratio of 1:0.05, and melt blending at 130° C. for 17 min to obtain a blend;

(4) The blend obtained in step (3) is placed in a vacuum oven and vacuum dried at 80° C. for 12 h to obtain a white block product, which is an oil-soluble viscosity reducer S3. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 6:1.

The viscosity reducer S3 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 25 through scanning electron microscopy analysis.

The infrared absorption spectrum of viscosity reducer S3 was tested. Compared with the infrared absorption spectrum of polymer C2, the maximum absorption peak intensity (P1) of the viscosity reducer at 691 cm ^-1 was significantly enhanced, indicating that PMMA microspheres were combined with the polymer through hydrogen bonding.

In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 691 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2849 cm ^-1 is 0.34.

Example 4

(1) octadecyl acrylate and maleic anhydride monomers were weighed in a molar ratio of 2:1 and added to a flask, and toluene solvent was added in a ratio of toluene to the total mass of the monomers of 3:1, the temperature of the oil bath was controlled to be 40° C. and mechanical stirring was applied at a constant rate, the stirring rate was maintained at 500 rpm, and after stirring for 10 minutes to ensure that the monomers were completely dissolved in toluene, the oil bath temperature was adjusted to a reaction temperature of 80° C., and a benzamide peroxide solution (1 wt% of the monomer mass) was added dropwise, and the reaction time was controlled to be 8 hours to obtain a reaction product;

(2) The reaction product obtained in step (1) was poured into a 500 mL beaker, and 5 times the weight of methanol was added and stirred continuously until floccules precipitated at the bottom of the beaker, and the purified polymer C3 was obtained after filtration and drying. The composition structure of the polymer C3 was analyzed by hydrogen nuclear magnetic spectrum, and the peaks in the figure were attributed as follows: In ¹ H NMR, the chemical shifts at different displacements of δ0.9, δ1.3 and δ1.6 belong to The hydrogen proton peaks of -CH ₃ , -CH ₂ - and -CH- are different from those in Figure 1 . The hydrogen proton peak of -C=O-CH ₂ - is at δ4.0, and the hydrogen proton peak of maleic anhydride group is at δ3.5. The hydrogen proton peak at a chemical shift of 3.5 ppm proves the successful synthesis of polymer C3.

It is proved that the polymer C3 contains the structural unit A represented by formula (1) and the structural unit B represented by formula (2), wherein _R1 is a C18 straight-chain alkyl group, _R2 , _R3 , and _R4 are hydrogen atoms, _R5 and _R6 are connected to form anhydride, and _R7 and _R8 are hydrogen.

The GPC test showed that the weight average molecular weight of the polymer C3 was 11192 g/mol. The distribution coefficient method showed that the hydrophilic-lipophilic balance (HLB) value of the polymer C3 was 4.6.

(3) placing polymer C3 and PMMA microspheres P1 in a melt blender at a mass ratio of 1:0.05, and melt blending at 160° C. for 12 min to obtain a blend;

(4) The blend obtained in step (3) is placed in a vacuum oven and vacuum dried at 80° C. for 12 h to obtain a white block product, which is an oil-soluble viscosity reducer S4. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 8:1.

The viscosity reducer S4 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 27 through scanning electron microscopy analysis.

The viscosity reducer S4 was subjected to an infrared absorption spectrum test. Compared with the infrared absorption spectrum of the polymer C3, the maximum absorption peak intensity (P1) at 700 cm ^-1 was significantly enhanced. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 700 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2920 cm ^-1 was 0.35.

Example 5

(1) octadecyl acrylate and maleic anhydride monomers were weighed in a molar ratio of 5:1 and added to a flask, and toluene solvent was added in a ratio of toluene to the total mass of the monomers of 3:1, the temperature of the oil bath was controlled to be 40° C. and mechanical stirring was applied at a constant rate, the stirring rate was maintained at 500 rpm, and after stirring for 10 minutes to ensure that the monomers were completely dissolved in toluene, the oil bath temperature was adjusted to a reaction temperature of 80° C., and a benzamide peroxide solution (1 wt% of the monomer mass) was added dropwise, and the reaction time was controlled to be 8 hours to obtain a reaction product;

(2) pouring the reaction product obtained in step (1) into a 500 mL beaker, adding 5 times the weight of methanol and continuously stirring until floccules precipitate on the bottom of the beaker, filtering and drying to obtain a purified polymer C4; analyzing the composition structure of polymer C4 by hydrogen nuclear magnetic spectrum, proving that polymer C4 contains structural unit A represented by formula (1) and structural unit B represented by formula (2), wherein _R1 is a C18 straight-chain alkyl group, _R2 , _R3 , and _R4 are hydrogen atoms, _R5 and _R6 are connected to form anhydride, and _R7 and _R8 are hydrogen.

According to GPC test, the weight average molecular weight of the polymer C4 is 12030 g/mol. According to the distribution coefficient method, the hydrophilic-lipophilic balance (HLB value) of the polymer C4 is 4.2.

(3) Place polymer C4 and PMMA microspheres P1 in a melt blender at a mass ratio of 1:0.05 and melt blend at 160°C. Mix for 10 min to obtain a blend;

(4) The blend obtained in step (3) was placed in a vacuum oven and vacuum dried at 80° C. for 12 h to obtain a white block product, which is an oil-soluble viscosity reducer S5. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 3.4:1.

The viscosity reducer S5 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 20 through scanning electron microscopy analysis.

The viscosity reducer S5 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 730 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2960 cm ^-1 was 0.3.

Example 6

The method of Example 2 is followed, except that polymer C1 and PMMA microspheres P1 are placed in a melt blender at a mass ratio of 1:0.01, melt blended at 130°C for 14 minutes to obtain a blend; the obtained blend is placed in a vacuum oven and vacuum dried at 80°C for 12 hours to obtain a white block product, which is an oil-soluble viscosity reducer S6. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 28:1.

The viscosity reducer S6 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 12 through scanning electron microscopy analysis.

The viscosity reducer S6 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 697 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2900 cm ^-1 was 0.25.

Example 7

The method of Example 2 is followed, except that polymer C1 and PMMA microspheres P1 are placed in a melt blender at a mass ratio of 1:0.07, and melt blended at 140°C for 16 minutes to obtain a blend; the obtained blend is placed in a vacuum oven and vacuum dried at 80°C for 12 hours to obtain a white block product, which is the oil-soluble viscosity reducer S7.

The viscosity reducer S7 was characterized by scanning electron microscopy. Similar to Figures 5 and 6, the number of microspheres in the viscosity reducer in the area of 10 μm×10 μm was 54. In the viscosity reducer, both the matrix and the microspheres contained acrylic acid structural units, and the molar ratio of the same structural units contained in the two was 4:1.

The viscosity reducer S7 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 730 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2915 cm ^-1 was 0.36.

Example 8

The method of Example 2 is followed, except that the polymer C1 and the PMMA microspheres P1 are placed in a molten The obtained blend was placed in a vacuum oven and vacuum dried at 80°C for 12 hours to obtain a white block product, which is the oil-soluble viscosity reducer S7. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 3.1:1.

The viscosity reducer S7 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 75 through scanning electron microscopy analysis.

The viscosity reducer S7 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 710 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2920 cm ^-1 was 0.34.

Example 9

(1) Weighing octadecyl acrylate and maleic anhydride monomers in a molar ratio of 1:1 and adding them into a flask, and adding toluene solvent in a ratio of toluene to the total mass of the monomers of 3:1, controlling the temperature of the oil bath to 40° C. and applying mechanical stirring at a constant rate, maintaining the stirring rate at 500 rpm, stirring for 10 minutes to ensure that the monomers are completely dissolved in toluene, adjusting the oil bath temperature to a reaction temperature of 80° C., and adding benzamide peroxide (1 wt% of the monomer mass) solution dropwise, controlling the reaction time to 8 hours, and obtaining a reaction product;

(2) pouring the reaction product obtained in step (1) into a 500 mL beaker, adding 5 times the weight of methanol and continuously stirring until floccules precipitate on the bottom of the beaker, filtering and drying to obtain a purified polymer C5; analyzing the composition structure of the polymer C5 by hydrogen nuclear magnetic spectrum, it is proved that the polymer C5 contains the structural unit A represented by formula (1) and the structural unit B represented by formula (2), wherein _R1 is a C18 straight-chain alkyl group, _R2 , _R3 , and _R4 are hydrogen atoms, _R5 and _R6 are connected to form anhydride, and _R7 and _R8 are hydrogen.

The GPC test showed that the weight average molecular weight of the polymer C5 was 10980 g/mol. The hydrophilic-lipophilic balance (HLB) value of the polymer C5 was 5 as tested by the distribution coefficient method.

(3) placing polymer C5 and PMMA microspheres P1 in a melt blender at a mass ratio of 1:0.05, and melt blending at 160° C. for 10 min to obtain a blend;

(4) The blend obtained in step (3) was placed in a vacuum oven and vacuum dried at 80° C. for 12 h to obtain a white block product, which is an oil-soluble viscosity reducer S9. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 1.1:1.

The viscosity reducer S9 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 21 through scanning electron microscopy analysis.

The viscosity reducer S9 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 690 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2940 cm ^-1 was 0.36.

Example 10

(1) Weigh octadecyl acrylate and maleic anhydride monomers in a molar ratio of 7:1 and add them to a flask. The total mass ratio of 3:1 is 3:1, the temperature of the oil bath is controlled to be 40°C and mechanical stirring is applied at a constant rate, the stirring rate is maintained at 500 rpm, and after stirring for 10 minutes to ensure that the monomer is completely dissolved in toluene, the oil bath temperature is adjusted to a reaction temperature of 80°C, and a benzamide peroxide (1wt% of the monomer mass) solution is added dropwise, and the reaction time is controlled to be 8 hours to obtain a reaction product;

(2) pouring the reaction product obtained in step (1) into a 500 mL beaker, adding 5 times the weight of methanol and continuously stirring until floccules precipitate on the bottom of the beaker, filtering and drying to obtain a purified polymer C6; analyzing the composition structure of polymer C6 by hydrogen nuclear magnetic spectrum, proving that polymer C6 contains structural unit A represented by formula (1) and structural unit B represented by formula (2), wherein _R1 is a C18 straight-chain alkyl group, _R2 , _R3 , and _R4 are hydrogen atoms, _R5 and _R6 are connected to form anhydride, and _R7 and _R8 are hydrogen.

The GPC test showed that the weight average molecular weight of the polymer C6 was 12376 g/mol. The distribution coefficient method showed that the hydrophilic-lipophilic balance (HLB) value of the polymer C6 was 3.8.

(3) placing polymer C6 and PMMA microspheres P1 in a melt blender at a mass ratio of 1:0.05, and melt blending at 140° C. for 13 min to obtain a blend;

(4) The blend obtained in step (3) was placed in a vacuum oven and vacuum dried at 80° C. for 12 h to obtain a white block product, which is an oil-soluble viscosity reducer S10. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 6:1.

The viscosity reducer S10 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 20 through scanning electron microscopy analysis.

The viscosity reducer S10 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 705 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2920 cm ^-1 was 0.29.

Embodiment 11

(1) octadecyl acrylate and maleic anhydride monomers were weighed in a molar ratio of 10:1 and added to a flask, and toluene solvent was added in a ratio of toluene to the total mass of the monomers of 3:1, the temperature of the oil bath was controlled to be 40° C. and mechanical stirring was applied at a constant rate, the stirring rate was maintained at 500 rpm, and after stirring for 10 minutes to ensure that the monomers were completely dissolved in toluene, the oil bath temperature was adjusted to a reaction temperature of 80° C., and a benzamide peroxide solution (1 wt% of the monomer mass) was added dropwise, and the reaction time was controlled to be 8 hours to obtain a reaction product;

(2) pouring the reaction product obtained in step (1) into a 500 mL beaker, adding 5 times the mass of methanol and stirring continuously until floccules precipitate on the bottom of the beaker, filtering and drying to obtain a purified polymer C7; analyzing the composition structure of the polymer C7 by hydrogen nuclear magnetic spectrum, it is proved that the polymer C7 contains the structural unit A represented by formula (1) and the structural unit B represented by formula (2), wherein _R1 is a C18 straight-chain alkyl group, _R2 , _R3 , and _R4 are hydrogen atoms, _R5 and _R6 are connected to form anhydride, and _R7 and _R8 are hydrogen.

The GPC test showed that the weight average molecular weight of the polymer C7 was 16698 g/mol. The distribution coefficient method showed that the hydrophilic-lipophilic balance (HLB) value of the polymer C7 was 3.2.

(3) Place polymer C7 and PMMA microspheres P1 in a melt blender at a mass ratio of 1:0.05 and melt blend at 150°C. Mix for 15 min to obtain a blend;

(4) The blend obtained in step (3) was placed in a vacuum oven and vacuum dried at 80° C. for 12 h to obtain a white block product, which is an oil-soluble viscosity reducer S11. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 6:1.

The viscosity reducer S11 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 18 through scanning electron microscopy analysis.

The viscosity reducer S11 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 740 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2920 cm ^-1 was 0.21.

Example 12

The method of Example 2 is followed, except that at room temperature, polymer C1 and PMMA microspheres P1 are directly mixed at a mass ratio of 1:0.05 for 17 minutes to obtain a mixture viscosity reducer S12.

The viscosity reducer S13 was characterized by scanning electron microscopy. Microspheres were attached to the surface of the polymer and the dispersion uniformity was poor. Scanning electron microscopy analysis showed that there were 32 microspheres in the viscosity reducer in an area of 10 μm×10 μm.

The viscosity reducer S1 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) at 700 cm ^-1 to the maximum absorption peak intensity (P2) at 2920 cm ^-1 was 0.12.

Example 13

The method of Example 2 is followed, except that polymer C1 and PMMA microspheres P1 are placed in a melt blender at a mass ratio of 1:0.5, melt blended at 140°C for 15 minutes to obtain a blend; the obtained blend is placed in a vacuum oven and vacuum dried at 80°C for 12 hours to obtain a white block product, which is an oil-soluble viscosity reducer S13. In the viscosity reducer, both the matrix and the microspheres contain acrylic acid structural units, and the molar ratio of the same structural units contained in the two is 0.6:1.

The viscosity reducer S13 was characterized by scanning electron microscopy. Similar to FIG. 5 and FIG. 6 , the number of the microspheres in the viscosity reducer in an area of 10 μm×10 μm was 510 through scanning electron microscopy analysis.

The viscosity reducer S13 was subjected to an infrared absorption spectrum test. In the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 710 cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2920 cm ^-1 was 0.5.

Comparative Example 1

Put polyoctadecyl acrylate (weight average molecular weight of 7000 g/mol) and PMMA microspheres P1 in a melt blender at a mass ratio of 1:0.05, and melt blend at 130° C. for 17 min to obtain a blend;

The blend was then placed in a vacuum oven and vacuum dried at 80° C. for 12 h to obtain viscosity reducer DS1.

Comparative Example 2

A silicon-fluorine viscosity reducer (purchased from Shandong Jiaozhou Petroleum Additives Co., Ltd.) was used as the viscosity reducer DS2.

Comparative Example 3

PMMA microspheres P1 were directly used as the viscosity reducing agent, and were recorded as DS3.

Comparative Example 4

The polymer C7 prepared in Example 11 was directly used as a viscosity reducer and was recorded as DS4.

Test Case

Preparation of drilling fluid:

Preparation of synthetic drilling fluid: Take 240g of continuous phase base oil, add 9g of primary emulsifier and 3g of auxiliary emulsifier, stir at high speed for 60 minutes to fully dissolve them, add 60g of calcium chloride aqueous solution, stir at high speed for 60 minutes to form oil-in-water emulsion, then add 12g of organic soil, 3g of wetting agent, 10g of fluid loss reducer, 6g of alkaline regulator, stir for 20 minutes to fully dissolve them, add barite to increase the density to 1.8g/ ^cm3 , stir for 60 minutes to obtain synthetic drilling fluid.

(1) Used to illustrate that viscosity reducers can improve the resistance of drilling fluids to oil invasion

The viscosity reducers prepared in the above examples and comparative examples were added to the synthetic-based drilling fluid, and the amount of the viscosity reducer added was shown in Table 1 based on 100 parts by weight of the drilling fluid. Then, 20 wt% of crude oil from the E ₂ S ³ layer of the Paleogene of the Cenozoic Era in the Jiyang Depression was added to the synthetic-based drilling fluids, and the apparent viscosity, dynamic shear force and demulsification voltage of the drilling fluids were tested at 20°C using the standard test of "GB/T 16783.2-2012 Field Test of Drilling Fluids in the Petroleum and Natural Gas Industry Part 2: Oil-Based Drilling Fluids". The results are shown in Table 1.

Table 1

From the results in Table 1, it can be seen that adding the viscosity reducer provided by the present invention to the drilling fluid not invaded by crude oil can effectively improve the anti-oil invasion ability of the drilling fluid. Compared with the sample without the additive, the drilling fluid sample pre-added with the viscosity reducer has a lower increase in apparent viscosity and a smaller dynamic shear force after being invaded by crude oil, and can maintain suitable fluidity. While maintaining suitable fluidity, the drilling fluid invaded by crude oil can have better electrical stability. In a preferred case, it can take into account lower apparent viscosity, dynamic shear force and higher demulsification voltage, so as to be more conducive to the recycling of the drilling fluid.

(2) Used to illustrate the inhibitory effect of viscosity reducers on the viscosity increase of drilling fluids invaded by crude oil

At 65°C, 20wt% of crude oil was added to the synthetic-based drilling fluid, which was derived from ^the _E2S3 layer of the Paleogene of the Cenozoic Era in the Jiyang Depression. The drilling fluid invaded by crude oil was then cooled at room temperature, stirred for 5 minutes, and then the viscosity reducers of the above embodiments and comparative examples were added. The amount of the viscosity reducer was shown in Table 2 based on 100 parts by weight of the drilling fluid. After cooling to 20°C, the apparent viscosity of the drilling fluid was tested in accordance with GB/T16783.2-2012 "Field Test of Drilling Fluids in Petroleum and Natural Gas Industry Part 2: Oil-Based Drilling Fluids". The results are shown in Table 2.

Table 2

It can be seen from the results in Table 1 and Table 2 that the viscosity reducer provided by the present invention can be added to the drilling fluid that has not been invaded by crude oil, or can be added during the use of the drilling fluid or after being invaded by crude oil, and can play a role in improving the anti-oil pollution ability of the drilling fluid, and can effectively inhibit the viscosity increase of the drilling fluid invaded by crude oil.

The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims (14)

A viscosity reducer, characterized in that the viscosity reducer comprises a matrix, and particles attached to the surface of the matrix and/or wrapped in the matrix, wherein the matrix comprises a lipophilic part and a hydrophilic part; the particles do not melt below 100° C., and according to a scanning electron microscope analysis, in a viscosity reducer in an area of 10 μm×10 μm, the number of the particles is 1-1500. The viscosity reducer according to claim 1, wherein in the infrared absorption spectrum of the viscosity reducer, the ratio of the maximum absorption peak intensity (P1) in the region of 700±50cm ^-1 to the maximum absorption peak intensity (P2) in the region of 2920±70cm ^-1 is not less than 0.25, preferably 0.25-0.4. The viscosity reducer according to claim 1 or 2, wherein, according to a scanning electron microscope analysis, in the viscosity reducer in an area of 10 μm×10 μm, the number of the particles is 2-1000, preferably 5-500; Preferably, the mass ratio of the matrix to the particles is 1:(0.01-0.5), preferably 1:(0.02-0.07), and more preferably 1:(0.03-0.05). The viscosity reducer according to any one of claims 1 to 3, wherein the particle size is 300 nm-5 μm, preferably 400 nm-3 μm; Preferably, at 20°C, the lipophilicity of the particles is not less than 50%, preferably 50-70%. The viscosity reducer according to any one of claims 1 to 4, wherein the particles are selected from at least one of organic particles, inorganic oxide particles and organic-inorganic composite particles; Preferably, the particles are at least one of polymethyl methacrylate particles, polyethyl methacrylate particles, glycidyl methacrylate particles and polyethylene terephthalate particles, preferably polymethyl methacrylate particles. The viscosity reducer according to any one of claims 1 to 5, wherein the hydrophilic-lipophilic balance value of the matrix is 3 to 5; Preferably, the lipophilic part contains at least one lipophilic functional group, the hydrophilic part contains at least one hydrophilic functional group, and in the matrix, the molar ratio of the lipophilic functional group to the hydrophilic functional group is 8-90:1; Preferably, based on the total amount of the matrix, the content of the lipophilic functional group is 80-95 wt %. The viscosity reducer according to claim 6, wherein the lipophilic functional group is selected from at least one of a substituted or unsubstituted ester group, an alkyl group, an alkenyl group, an alkynyl group and an aryl group, preferably a C16-C22 alkyl group, an alkenyl group, an alkynyl group or an aryl group; and/or, The hydrophilic functional group is selected from at least one of a hydroxyl group, a carboxyl group, an acid anhydride group and an amino group. The viscosity reducer according to any one of claims 1 to 7, wherein the matrix and the particles contain the same structural units; Preferably, in the viscosity reducing agent, the ratio of the molar amount of the same structural unit contained in the matrix to the molar amount of the same structural unit contained in the particles is 1-30:1, preferably 5-15:1. The viscosity reducer according to any one of claims 1 to 8, wherein the matrix is a polymer, and the weight average molecular weight of the matrix is 5000-50000 g/mol, preferably 6000-30000 g/mol, and more preferably 8000-20000 g/mol. The viscosity reducer according to claim 9, wherein the matrix comprises a structural unit A as shown in formula (1) and a structural unit B as shown in formula (2);
wherein R ₁ , R ₂ , R ₃ , and R ₄ are each independently selected from a hydrogen atom, a C16-C22 alkyl group, a C16-C22 alkenyl group, a C16-C22 alkynyl group, or a C16-C22 aryl group, and at least one of R ₁ , R ₂ , R ₃ , and R ₄ is not a hydrogen atom; R ₅ , R ₆ , R ₇ , and R ₈ contain at least one hydroxyl group, carboxyl group, or amino group, or R ₅ and R ₆ are connected to form an acid anhydride, or R ₇ and R ₈ are connected to form an acid anhydride; Preferably, in the polymer, the molar ratio of the structural unit A to the structural unit B is (1-10):1, preferably (2-5):1. A method for preparing a viscosity reducer comprises: mixing a matrix with particles in a molten state and then drying; the matrix comprises a lipophilic part and a hydrophilic part; the particles do not melt below 100°C, and the mass ratio of the matrix to the particles is 1:(0.01-0.5). The preparation method according to claim 11, wherein, preferably, the size of the particles is 300 nm-5 μm; Preferably, the mass ratio of the matrix to the particles is 1:(0.02-0.07), more preferably 1:(0.03-0.05); Preferably, the mixing conditions include: the mixing temperature is 100-180°C, preferably 120-160°C, and the mixing time is 5-30min, preferably 10-20min; Preferably, the drying is carried out under vacuum conditions, at a temperature of 60-80° C., for a time of 10-12 h. Use of the viscosity reducer according to any one of claims 1 to 10 or the viscosity reducer prepared by the preparation method according to claim 11 or 12 in reducing the viscosity of crude oil invading drilling fluid. A method for improving the ability of drilling fluid to resist oil pollution, characterized in that the method comprises adding the viscosity reducer according to any one of claims 1 to 10 or the viscosity reducer prepared by the preparation method according to claim 11 or 12 to the drilling fluid; Preferably, the drilling fluid is an oil-based drilling fluid or a synthetic-based drilling fluid; Preferably, the amount of the viscosity reducer is 0.05-1 part by weight, preferably 0.1-0.5 part by weight, relative to 100 parts by weight of the drilling fluid.